In recent years, to reduce power consumption, many semiconductor integrated circuits are supplied with power supply voltages from different power supplies in units of domains divided for a plurality of functional modules. For example, if a semiconductor integrated circuit includes two domains D1 and D2, the domain D1 is supplied with a power supply voltage V1 from a power supply S1, and the domain D2 is supplied with a power supply voltage V2 from a power supply S2 different from the power supply S1.
Herein, if the power supply voltages V1 and V2 have different values, the respective clock phases in the domains D1 and D2 differ from each other in timing in the exchange of signals between the domains D1 and D2, and thus accurate exchange of signals may be prevented. In this case, therefore, the exchange of signals between the domains D1 and D2 is performed via an asynchronous bridge unit which performs signal level conversion and clock domain crossing.
Meanwhile, if the power supply voltages V1 and V2 have the same value, the exchange of signals is performed with the asynchronous bridge unit bypassed. Thus, data transmission may be performed more efficiently than in the exchange of signals via the asynchronous bridge unit. Even in this case, however, if the clock frequency of a power supply is substantially changed, for example, the power supply voltage may fluctuate owing to a steep current fluctuation occurring in the power supply. In that case, the respective values of the power supply voltages V1 and V2 differ from each other, and thus it is difficult to perform the exchange of signals by bypassing the asynchronous bridge unit. In view of this, describes a technique is described which, when performing the exchange of signals by bypassing the asynchronous bridge unit, supplies two domains D1 and D2 with power supply voltages from a single power supply S1 (or S2) (see, e.g., Japanese Laid-open Patent Publication No. 2008-204271).